The present invention relates to semiconductor processes and, more particularly, to a metallization process for reducing the stress existing between the Alxe2x80x94Cu layer and the titanium nitride (TiN) layer, and solving a galvanic problem.
In fabricating a multi-level interconnecting structure, aluminum alloys of low resistance and good adhesion to SiO2 are used to form the wiring layer. In common use of Alxe2x80x94Cu alloy, since Cu ions can prevent problems of spiking and electromigration, an Alxe2x80x94Cu wiring layer has good reliability. In the conventional metallization process, a Ti layer serving as a barrier layer, an Alxe2x80x94Cu layer, and a titanium nitride layer serving as an anti-reflective layer are sequentially deposited on a wafer. Then, using a patterned photoresist layer as a mask, the titanium nitride/Alxe2x80x94Cu/Ti layers are patterned to form the wiring line. However, the titanium nitride/Alxe2x80x94Cu/Ti layers are deposited in the same high-vacuum system, but in different sputtering chambers with different process temperatures, wherein the Alxe2x80x94Cu layer is deposited at 270xc2x0 C. and the titanium nitride layer is deposited at room temperature. Therefore, at the beginning of sputtering titanium nitride, the wafer with the Alxe2x80x94Cu layer is still in a high-temperature state and thermal stress is produced between the Alxe2x80x94Cu layer and the titanium nitride layer, resulting cracks on the titanium nitride layer. Furthermore, in the subsequent photolithography process, the developer solution easily infiltrates from the cracks to the Alxe2x80x94Cu layer to cause an oxidation-reduction reaction. As a result, a galvanic corrosion occurs in the wiring layer. This leads to defective circuits.
Seeking to solve the above-described problem, U.S. Pat. No. 5,994,217 discloses a method of employing annealing for releasing the stress existing between the titanium nitride layer and Alxe2x80x94Cu layer. However, adding the step of annealing increases the thermal budget and decreases the property of the semiconductor device. In another disclosed method, prior to the deposition of the titanium nitride layer, the wafer with the Alxe2x80x94Cu layer is cool down by taking it out from the vacuum system. But, this substantially reduces the yield.
Embodiments of the present invention are directed to a metallization process for reducing the stress existing between the Alxe2x80x94Cu layer and the titanium nitride (TiN) layer, and solving the galvanic problem. The process does so by cooling the wafer in the vacuum apparatus where the metallization process is performed after formation of the Alxe2x80x94Cu layer and before the formation of the TiN layer. The wafer may be cooled, for instance, by fanning the wafer with an inert gas. In some embodiments, the wafer is transferred from the Alxe2x80x94Cu sputtering chamber to the titanium nitride sputtering chamber after formation of the Alxe2x80x94Cu layer at a high temperature. The wafer is cooled in the titanium nitride sputtering chamber before formation of the TiN layer, by introducing an inert gas into the titanium nitride sputtering chamber.
In accordance with an aspect of the present invention, a metallization process comprises placing a wafer in an Alxe2x80x94Cu sputtering chamber to form an Alxe2x80x94Cu layer on the wafer, and transferring the wafer to a titanium nitride sputtering chamber. An inert gas is introduced into the titanium nitride sputtering chamber to cool the wafer. A titanium nitride layer is formed on the Alxe2x80x94Cu layer of the wafer in the titanium nitride sputtering layer after cooling the wafer.
In some embodiments, the Alxe2x80x94Cu layer is formed at a temperature of about 260-280xc2x0 C., and the titanium nitride layer is formed on the Alxe2x80x94Cu layer at a temperature of about room temperature. The inert gas may comprise nitrogen or argon. The inert gas is injected into the titanium nitride sputtering chamber to fan the wafer until the wafer is cooled to a temperature of about 60-80xc2x0 C. In specific examples, the inert gas is introduced into the titanium nitride sputtering chamber at a flow rate of about 80-120 sccm and a flow time of about 20-30 seconds. The inert gas introduced into the titanium nitride sputtering chamber to cool the wafer is terminated before forming the titanium nitride layer. The Alxe2x80x94Cu sputtering chamber and the titanium nitride sputtering chamber are typically contained in a sputtering apparatus at a vacuum state.
In accordance with another aspect of the present invention, a method for forming a wiring line comprises placing a wafer in a Ti sputtering chamber to form a Ti layer on the wafer, and transferring the wafer to an Alxe2x80x94Cu sputtering chamber to form an Alxe2x80x94Cu layer on the Ti layer. The wafer is transferred to a titanium nitride sputtering chamber. An inert gas is introduced into the titanium nitride sputtering chamber to cool the wafer. A titanium nitride layer is formed on the Alxe2x80x94Cu layer of the wafer in the titanium nitride sputtering layer after cooling the wafer.
Another aspect of the invention is directed to a metallization process performed in a vacuum sputtering apparatus which includes an Alxe2x80x94Cu sputtering chamber and a titanium nitride sputtering chamber. The metallization process comprises placing a wafer in an Alxe2x80x94Cu sputtering chamber to form an Alxe2x80x94Cu layer on the wafer, cooling the wafer in the vacuum sputtering apparatus to a preset temperature, and transferring the wafer to a titanium nitride sputtering chamber. A titanium nitride layer is formed on the Alxe2x80x94Cu layer of the wafer in the titanium nitride sputtering chamber after cooling the wafer. The preset temperature is sufficiently low to reduce thermal stresses between the titanium nitride layer and the Alxe2x80x94Cu layer so as to substantially prevent cracks from forming in the titanium nitride layer.
In some embodiments, the wafer is cooled by fanning the wafer with an inert gas. The wafer may cooled after transferring the wafer to the titanium nitride sputtering chamber, for instance, by introducing the inert gas into the titanium nitride sputtering chamber to fan the wafer with the inert gas.